Discussion on: Impeachment in a functional way

Kleisli composition! :)

It's great to see another F# developer here. I learned something new from your code when I saw the fish operator defined as an infix function that takes three arguments. I didn't even know that was possible. I guess F# knows that the >=> always goes between the first two arguments? I found it a little easier to understand when I rewrote mentally it as:

let (>=>) a b =
    fun x ->
        match a x with
        | Impeach v -> b v
        | DontImpeach reason -> DontImpeach(reason)

Your version is shorter and cleaner, though, so I certainly don't object.

The other thought I had is a minor suggestion. Functions that match on their last argument are a pretty common pattern in F#, so there's a bit of syntactical sugar you can use if you want to tighten them up. Instead of this:

let tryInSenate exitAt =
    match exitAt with
    | Trial -> DontImpeach (Reason "Senate trial exonerated the President")
    | _ -> Impeach exitAt

You can write:

let tryInSenate = function
    | Trial -> DontImpeach (Reason "Senate trial exonerated the President")
    | exitAt -> Impeach exitAt

Of course, the downside to this approach is that the argument disappears entirely ("point-free" style), which can make the code harder to understand. Just wanted to mention it as an idea.

Lastly, on a purely humorous note, since you're concerned about the bias of using the Result type, you missed a great opportunity to use a Haskell-style Either type instead, since its constructors are Left and Right!